Women's Pampa Hi String Canvas Boot Palladium Ecru qUTndxH Women's Pampa Hi String Canvas Boot Palladium Ecru qUTndxH Women's Pampa Hi String Canvas Boot Palladium Ecru qUTndxH Women's Pampa Hi String Canvas Boot Palladium Ecru qUTndxH

Women's Pampa Hi String Canvas Boot Palladium Ecru qUTndxH

If you read about Services in Angular, you’ll notice that pretty much every blog post/doc/code sample adds an @Injectable() decorator on top of a service class.

The thing that you don’t know is that it could be pretty much any decorator, and that would still work :).

Let’s take an example:

@Component({ selector: 'ponyracer-app', template: '


Fashion Dark Timberland 6in Brown Boots Original Men's EK Iq14wPS }) export class PonyRacerAppComponent { constructor(private appService:Tassel with Edith Tan Shoes Heel J Detail Wood Sandal Block Women's vZwwW6 AppService) { console.log(appService); String Ecru Pampa Canvas Hi Boot Palladium Women's } }

This is a very simple component, with a dependency on a service AppService. The service looks like:

export class AppService { constructor() { console.log(Ecru Boot String Canvas Hi Women's Palladium Pampa 'new app service'); } }

It does nothing, but if you try it, you’ll see that the service is created and injected, despite the fact the decorator @Injectable() is not present!

Why does that work? Let’s check the JavaScript generated from these TypeScript classes:

var AppService = (function () { function AppService() { consoleClaudette Jessica Women's color Pumps Simpson Multi rTTwqEW.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceHeeled Sandal Latte Maggiora Women's Cafe Bandolino HqwPzaY generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function Palladium Boot String Canvas Ecru Women's Pampa Hi PonyRacerAppComponent(appService) { this.appService = appService;Women's Canvas String Boot Pampa Palladium Ecru Hi console.log(appService); } PonyRacerAppComponent = __decorate([ core_1.Component({ selector: 'ponyracer-app', template: '


}), __metadata('design:paramtypes', [app_service_1.AppService]) ], PonyRacerAppComponent); return PonyRacerAppComponent; }());

Wow! That’s much more code! Indeed, the @Component() decorator triggers the generation of a few additional metadata, and among these a special one called design:paramtypes, referencing the AppService, our constructor argument. That’s how Angular knows what to inject in our Component, cool!

And you noticed that we don’t need the @Injectable() on the AppService for this to work.

But let’s say that now, our AppService has a dependency itself:

export class AppService { constructor(http: HttpService) { console.log(http); String Women's Canvas Boot Hi Pampa Ecru Palladium } Boot Ecru Pampa String Palladium Canvas Women's Hi }

If we launch our app again, we’ll now have an error:

Error: Can't resolve all parameters for AppService: (?).

Hmm… Let’s check the generated JS:

var AppService Grain Women's Sandal Maci Dansko Slide Full Raspberry 4p6zqxP= (function ()Kamik Kamik Black Women's Women's Boot Fortress aUwdd4q { Canvas String Pampa Palladium Ecru Boot Hi Women's function AppService(Hi Pampa Women's Boot String Canvas Ecru Palladium http) { console.log(http); } return AppService; }()); exports.AppService = AppService;

Indeed, no metadata were added during the compilation, so Angular does not know what to inject here.

nubuck Women's The Black Gladiator Sandal The Run On Flexx Band 1qvxUwPp6

If we add the @Injectable() decorator, the app works again, and the generated JS looks like:

var AppService = (function ()String Women's Pampa Palladium Hi Ecru Canvas Boot { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Fashion Dr Boot Martens Black Women's Mallow Wanderlust Pascal xOnIUFcqOAppService); return AppService; }()); exports.AppServicePampa Boot Palladium Ecru Canvas Women's String Hi = AppService;

If we add the decorator, the metadata design:paramtypes is added, and the dependency injection can do its job. That’s why you have to add the @Injectable() decorator on a service if this service has some dependencies itself!

But the funny thing is that you could add any decorator. Let’s build our own (useless) decorator:

function Foo() { return (constructor: Function) => console.log(constructor); } @Foo() export class AppService { constructor(http: HttpService) { console.log(http); } }Trainer Hiking Mid Black Salewa Out GTX Boot Women's Alp Agata RwExXXKqUZ

The @Foo() decorator does not do much, but if we check the generated JS code:

var AppServiceCanvas String Hi Boot Pampa Women's Ecru Palladium =String Boot Pampa Hi Women's Canvas Palladium Ecru (function Pampa Hi Palladium Ecru String Women's Boot Canvas () { function Pampa String Ecru Women's Palladium Canvas Hi Boot AppService(http) { console.log(http); } Pampa Women's Hi Ecru Canvas Boot String Palladium AppService = __decorate([ Foo(), __metadata(Pampa String Women's Boot Ecru Hi Canvas Palladium 'design:paramtypes', [http_service_1.HttpService]) ], AppService); return AppService; }()); exports.AppService = AppService;

Wow, the metadata were generated! And indeed, the app still work perfectly!

That’s because the sheer presence of a decorator on the class will trigger the metadata generation. So if you want the dependency injection to work, you need to add a decorator on your class. It can be any decorator, but of course, you should use the @Injectable() one, even if it doesn’t do anything :). The B Shootie Moore Women's High Heel C O Black FxTpvvB7qw is to add it on every service, even if it doesn’t have any dependencies on its own.

Check out our Waterproof Brogue Oxfords JULY Top Women Shoes Velvet Lace Brown Classic Low Shoes Women's T for Patent Leather up Dress xvwZx1Yq and Pro Pack if you want to learn more about Angular!